Damp Or Mould After Cavity Wall Insulation

What's happening?

Cavity wall insulation fills the gap between the two layers of a wall. If rain gets into the outer leaf and the cavity is bridged, by mortar droppings, debris or the insulation itself, water can cross to the inner wall and show as damp. This is most likely where the wall is exposed to driving rain, the outer brick is cracked or badly pointed, or the property was not suitable. In other cases the fill has settled and left a gap at the top of the wall, which is a cold spot where condensation and mould form. Insulation can also make a house less ventilated, so condensation gets worse. The cause is not always the insulation: some damp was there already and became noticeable. Cavity wall insulation work is usually covered by a 25 year guarantee.

What usually causes it?

• Rain crossing a bridged cavity to the inner leaf, especially in exposed locations
• Cracked, eroded or badly pointed outer brickwork letting water in
• Insulation that has settled, leaving cold gaps near the top of the wall
• A house not suitable for cavity insulation, such as one with a very exposed aspect or a failing outer leaf
• Condensation worsened because the house became more airtight with no extra ventilation
• A pre-existing leak or damp problem that was hidden before

Is it dangerous?

Damp and mould can affect health and the building, so do not wait. Do not remove the insulation yourself or paint over the damp before the cause is found: that can undo a claim.

Can I fix it myself?

Find the paperwork: the guarantee certificate, the installer's name and the date of the work. Photograph the damp and when it appears. Ventilate and heat the room and keep the outside wall clear. Check gutters, downpipes and the outside of the wall for cracks and failed pointing. Contact the installer in writing.

When should you call a damp proofer?

Call the original installer first, and the guarantee provider if they do not respond. CIGA provides a 25 year guarantee on cavity wall insulation fitted by its members. If the work was solid wall insulation through a government scheme, GOV.UK says to contact Ofgem. Then call an independent damp surveyor to find the cause.

What will the damp proofer actually do?

• Inspect the wall inside and out and check the pointing, render and gutters
• Test with a borescope or small inspection holes to see the cavity and the fill
• Measure moisture patterns and compare them with the weather and ventilation
• Say whether the cause is a bridged cavity, settled fill, penetrating damp or condensation
• Repair the outer wall, clear or extract the affected fill or top it up where needed
• Improve ventilation and treat mould, then dry out and re-decorate

Who fixes this

• Damp survey
• Penetrating damp repair
• Condensation and mould treatment

Questions people ask

Sources & References

1. CIGA: cavity wall insulation guarantee
2. GOV.UK: what to do if you have poor quality wall insulation
3. TrustMark: complaints process
4. Property Care Association: penetrating damp